INDIANAPOLIS - First came the leg injury that delayed Trey Lyles' inclusion in Kentucky's platoon system until the fall. A midseason bout of strep throat followed, sidelining him for three games.

The impressive performances between those absences are why coach John Calipari says the 6-foot-10 Lyles is the "X-factor" for the top-ranked Wildcats.

Several players have worn that label this season for Kentucky (38-0). But it particularly fits Lyles because his athleticism makes him difficult to defend or beat, creating another matchup problem for opponents already struggling to contain Wildcats 7-footer Willie Cauley-Stein and 6-11 Karl-Anthony Towns.

"I'm just going out there and doing what [Calipari] asks me to do," said Lyles, who has no problem with the X-factor label. "He tells me all the time to just execute and play hard."

Lyles has been playing some of his best basketball in the NCAA tournament, averaging 11.1 points, and 7.3 rebounds. He is a threat that Wisconsin must neutralize the Final Four rematch Saturday in Indianapolis, Lyles' hometown. The winner will face whoever advances in the Michigan State-Duke matchup in the other semifinal game.

Kentucky's frontcourt is a challenge for most teams, and Lyles' versatility further complicates things. His quickness allows him to play inside and on the perimeter. His 11-point, 11-rebound effort in a 64-51, round-of-32 victory over Cincinnati included a dunk and a spin move for a basket that helped the Wildcats retain momentum against the physical Bearcats.

He's playing small forward, but can slide over to power forward, or even center depending on the matchup. Lyles tries to get Kentucky's other post players involved, though Calipari believes his strength is finishing, not facilitating.

Lyles wants to finish better than he did in the regional final. He's motivated to move on from what he thinks was a subpar nine-point, five-rebound effort in the 68-66 win over Notre Dame.

Kentucky still managed to cut down the nets and advance.

"It was great, being out there and having fun," Lyles said of the postgame celebration. "There was a little relief after that game, but we're focused on the next one now."